Microphone Noise Suppression Using Adaptive Filter Coefficient Control
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Solution Overview
Problem
Conventional microphone devices struggle to effectively suppress noise from multiple directions and multiplicative noise, leading to poor sound quality and recognition errors in noisy environments, especially when dealing with reflected waves and multiple noise sources.
Innovation Solution
A microphone device with a signal generating section, determining section, adaptive filter section, and noise suppressing section that generates a main signal and noise reference signal to suppress noise, using an adaptive filter to learn filter coefficients only when the target sound is dominant and corrects frequency distortion caused by reflected waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional microphone devices use simple signal combining methods, then the device complexity is low, but the noise suppression capability from multiple directions is insufficient
Solution Approach 1:
The patent segments the noise suppression task by separating direct noise sources from reflected noise sources. Direct noise is suppressed using conventional methods while reflected noise is handled separately through reflection characteristic correction, allowing each subsystem to focus on a specific aspect of noise suppression.
Solution Approach 2:
The patent introduces a reflection characteristic correction section as an intermediary component that processes reflected noise separately. This mediator corrects the frequency characteristics distorted by reflections before the final noise suppression, enabling effective suppression of reflected noise without compromising the simplicity of the overall system.
2Adaptability or versatility
If the adaptive filter learns filter coefficients continuously, then the noise suppression adapts to changing noise patterns, but the processing time increases and stability decreases in noisy environments
Solution Approach 1:
The patent implements periodic action by controlling the adaptive filter to learn filter coefficients only during specific periods when the target sound is dominant. The determining section periodically evaluates the sound environment and enables coefficient learning only when necessary, preventing continuous processing during noisy periods when stability is compromised.
Solution Approach 2:
The patent uses feedback through the determining section that continuously monitors the sound environment and provides feedback to control the adaptive filter's operation. This feedback mechanism enables the system to adapt to changing noise patterns by activating coefficient learning only when the target sound is dominant, while maintaining stability during noisy conditions.
3Manufacturing precision
If the microphone device does not correct for reflected waves, then the device complexity is low, but the frequency characteristic distortion from reflections is not corrected
Solution Approach 1:
The patent applies preliminary action by having the reflection characteristic correction section process reflected noise before the final noise suppression stage. This preliminary correction of frequency characteristics caused by reflections ensures accurate frequency response while the main noise suppression handles the remaining noise, dividing the processing into distinct preliminary and final stages.
Data Source
AI summary
A signal generating section generates a main signal and a noise reference signal. A determining section determines whether a level ratio is larger than a predetermined value. An adaptive filter section generates a signal indicative of a signal component of a target sound included in the noise reference signal generated by the signal generating section, and learns a filter coefficient only when the determining section determines that the level ratio is larger than the predetermined value. A subtracting section subtracts the signal generated by the adaptive filter section from the noise reference signal. A noise suppressing section suppresses a signal component of noise included in the main signal by using the main signal and the noise reference signal after subtraction by the subtracting section.